The invention relates generally to the etching of servo tracks on magnetic data storage media. More particularly, the present invention relates to etching servo tracks on magnetic data storage media using multiple etching beams of laser energy provided from a source beam.
Servo patterns are used to control movement of read/write heads over magnetic data storage media where the media is provided in the form of a circular disk or a tape. The servo patterns on conventional magnetic data storage media, e.g., disks and tapes, are typically provided by magnetically encoding the magnetic coating provided on the substrate of the media.
Magnetic data storage disk systems have been developed that combine magnetic disk recording techniques with high track capacity optical servo patterns and drive systems. In use, an optical servo pattern is pre-recorded on a magnetic floppy disk in the form of a large number of equally spaced concentric tracks about the rotational axis of the disk. Data is stored in the magnetic tracks between the optical servo tracks using conventional magnetic recording techniques. An optical servo mechanism is provided to guide the magnetic read/write head accurately over the data between the optical servo tracks. By utilizing optical servo techniques, much higher track densities are achievable on a relatively inexpensive and typically removable magnetic media. In addition, the servo pattern is not subject to erasure or other degradation from external magnetic fields as are magnetic servo patterns.
The optical servo patterns used on disks may include a large number of equally spaced concentric tracks about the rotational axis of the disk or they may be provided as a continuous spiral track extending from the inside diameter of the disk to the outside diameter of the disk. U.S. Pat. No. 4,961,123 discloses optical servo patterns in which the tracks may be a single continuous groove, a plurality of equally spaced circular pits, or a plurality of short equally spaced grooves or stitches.
A number of techniques for forming the optical servo patterns on the magnetic data storage disks have been developed. U.S. Pat. No. 5,067,039 discloses a method for stamping the servo tracks on the magnetic media using a master stamping disk. U.S. Pat. No. 4,633,451 discloses a method of providing optical servo information on a magnetic medium including a multi-layer film. The optical servo tracks are formed on the multi-layer film by causing a reaction or interdiffusion to occur between layers. The reaction produces a reflectivity contrast between the exposed and unexposed areas. Other methods for manufacturing servo tracks are mentioned, including contact printing, embossing, and lithography.
Another approach to providing laser-etched optical servo tracks on magnetic data storage disks involves contact lithography, i.e., masking the area over which the servo pattern is to be formed, followed by directing laser energy over the masked area. See, e.g., U.S. Pat. Nos. 5,501,944 and 5,633,123. The mask includes openings or transparent areas to allow ablation of the disk surface such that an optical servo pattern is formed on the disk. Disadvantages of this approach include the requirement for a high power laser source and the difficulties in manufacturing the masks.
U.S. Pat. No. 4,961,123 discloses a method and apparatus for etching an optical servo pattern on a disk using a single focused beam of light energy. The magnetic disk is placed on a platen and rotated. A beam of light is focused to a small spot on the spinning data storage disk. The focused beam has sufficient intensity to ablate the disk surface at the spot, thereby reducing the reflectivity of the surface at that spot. As the disk rotates, a groove is produced. The beam can be left on during an entire revolution to produce a continuous groove, or it can be modulated on and off through one revolution to produce a stitched pattern of non-continuous grooves.
In systems and methods in which the optical servo pattern is etched using laser energy, the width of the etched grooves that define each servo track is a function of the energy density delivered by the incident beam to the focused spot relative to the ablation threshold of the media and the focused spot size.
Typically, the groove width in optical servo patterns is on the order of micrometers and must be maintained within tight tolerances. For a single servo track, the energy density at the focused spot and, therefore, the width of the groove (or grooves, with a stitched pattern) can be held constant simply by rotating the disk at a constant angular velocity. As the incident beam is moved radially on the disk surface to etch servo tracks at other radii, the change in radius results in a proportional change in the linear velocity of the disk surface at those radii. Therefore, if the disk rotates at a constant angular velocity, the energy density delivered to the surface of the disk will vary at different radii. To compensate for the varying energy density, it may be desirable to vary the beam intensity based on the linear velocity of the disk at different radii.
One disadvantage of the known systems and methods for laser etching of optical servo patterns is the limitation of producing a single track in an optical servo pattern at one time. As a result, the single beam of laser energy must be traversed over essentially the entire surface of the magnetic data storage disk to produce the entire optical servo pattern. That limitation can reduce throughput in the systems used to manufacture the magnetic data storage disks, thereby increasing the manufacturing costs.
As for the magnetically-encoded servo patterns, the magnetic nature of the patterns may preclude bulk erasing and reformatting by users because such actions could irreversibly destroy the magnetic servo pattern. Furthermore, the equipment required to write magnetic servo patterns on magnetic data storage tapes is costly and can only operate at relatively low speeds, thereby limiting throughput.
The present invention provides methods and systems for laser etching of optical servo patterns on magnetic data storage media using two or more beams of laser energy produced from a single source of laser energy to produce a servo pattern on the magnetic data storage media. By using two or more etching beams, the time required to produce a servo pattern on the magnetic data storage media can be significantly reduced. Alternatively, each servo track in the servo pattern can be written more than once.
The servo patterns thus formed can be read optically or they may be read magnetically using magnetic overwriting (if the servo pattern is formed in a magnetic coating on the media). In either case, the servo patterns are either permanently formed in the media when read optically, or they can be recreated after bulk erasing if they are provided using magnetic overwriting. In yet another alternative, the servo patterns may be read both magnetically and optically, with the magnetic and optical reading occurring simultaneously or sequentially.
In one aspect, the present invention provides a method of laser etching a servo pattern on magnetic data storage media by providing a source beam of laser energy; separating the source beam of laser energy into two or more etching beams; directing the etching beams onto the magnetic data storage media, whereby at least two servo tracks in the servo pattern are written simultaneously on the magnetic data storage media.
In another aspect, the present invention provides a method of laser etching a servo pattern on a magnetic data storage disk by providing a source beam of laser energy; separating the source beam of laser energy into two or more etching beams; directing the etching beams onto a magnetic coating on the magnetic data storage disk, wherein the etching beams remove at least a portion of the magnetic coating in ablated regions defined by the servo pattern; and rotating the magnetic data storage disk relative to the etching beams, whereby at least two servo tracks in the servo pattern are written simultaneously on the magnetic data storage disk.
In another aspect, the present invention provides a method of laser etching a servo pattern on a magnetic data storage tape by providing a source beam of laser energy; separating the source beam of laser energy into two or more etching beams; directing the etching beams onto a magnetic coating on the magnetic data storage tape, wherein the etching beams remove at least a portion of the magnetic coating in ablated regions defined by the servo pattern; and translating the magnetic data storage tape relative to the etching beams, whereby at least two servo tracks in the servo pattern are written simultaneously on the magnetic data storage tape.
These and other features and advantages of the present invention are described more completely below in connection with the illustrated embodiments presented.